Fuel cells, such as hydrogen fuel cells, are one possible alternative energy source for powering vehicles. In general, fuel cells include a negative electrode (anode), an electrolyte, and a positive electrode (cathode). In a proton exchange membrane fuel cell (PEMFC), the electrolyte is a solid, proton-conducting membrane that is electrically insulating but allows protons to pass through. Typically, the fuel source, such as hydrogen, is introduced at the anode using a bipolar or flow field plate where it reacts with a catalyst and splits into electrons and protons. The protons travel through the electrolyte to the cathode and the electrons pass through an external circuit and then to the cathode. At the cathode, oxygen in air introduced from another bipolar plate reacts with the electrons and the protons at another catalyst to form water.
During operation of the system, the water byproduct may accumulate in the fuel cell stack. If left in the fuel cell stack to be influenced by cold ambient temperatures, the water may freeze. To prevent frozen water from accumulating, fluid can be sent through the fuel cell to remove materials from the fuel cell stack when the vehicle is shut down in a process known as fuel cell purging.